The present invention generally relates to the field of optical motion detectors and more particularly to detecting motion with the ability to distinguish among incandescent, fluorescent, and near-infrared ambient lighting conditions.
There are many benefits afforded by the application of automation in the physical security and surveillance role. The advantages of a system that will not tire, become distracted, frightened, or even subversive are obvious. Potential functions assigned to an automated system can be categorized into three general areas: (1) detection, (2) verification, and (3) assessment. Detection is readily addressable by a multitude of commercially available sensors which can detect, for example, vibration, heat, sound, light, and motion. Verification involves evaluating the outputs of multiple sensors to lessen the probability of a false alarm. The assessment function responds to data provided by the sensors to ascertain the nature of the disturbance, usually in order to determine if a response is necessary.
The types of sensors employed in an automated security system are dependent upon the specific application. Such sensors include those specifically configured to detect intruders. Intrusion is most easily recognized through the use of some type of motion detection scheme; several exist.
A very simple type of passive motion detector responds to changes in background light level. One such detector is a Sprague D-1072 which is a 16 pin DIP (dual inline package) integrated circuit which incorporates a built-in lens that enable it to receive data within a cone-shaped detection field. After a brief settling period upon power-up, the D-1072 adjusts itself to ambient light conditions and establishes a reference condition. Any subsequent deviations from that reference will result in an alarm output. The low cost and directional field-of-view of that device allow them to be arrayed in order to establish unique detection zones which can pinpoint the relative position of a suspected security violation. The ability to provide geometric resolution of the intruder's position can be invaluable in tailoring an appropriate response in minimal time.
However, the D-1072 suffered two significant drawbacks which limited its utility and contributed to its eventual discontinuation. The current consumption of the device is in excess of 200 milliamps per unit, which is too large for practical battery powered operation. Also, it responded only to visible light. Furthermore, the D-1072 was incapable of sensing near-infrared light of the optical spectrum. Therefore, an intruder using an active-source night vision device would not trigger an alarm even if the night vision illumination source was directed at the sensor at point blank range. There are no systems in place even today at high security facilities employing elaborate automated security systems which warn that an area is being illuminated with near-infrared light.
Thus, a need exists for an optical motion detector which can detect surveillance by night vision devices.